Various techniques have been used in the past to produce stereoscopic (three-dimensional) images for motion pictures or television. In general, these techniques involve two camera systems in which two different pictures are taken from slightly different camera angles and locations. The object is to simulate the manner in which depth is perceived by a pair of human eyes, which are themselves slightly offset from each other and thus view images at slightly different angles. The two camera images are superimposed and presented to the viewer simultaneously on a television or movie screen. The images are then separated in some fashion for the viewer so that one eye sees only one image, and the other eye sees only the other image.
One technique which has been used to implement this approach is called the anaglyphic 3-D process, and has been employed in earlier 3-D motion pictures. This technique uses color filters to separate the two images. The images are color coded, for example with red and blue/green, respectively, and the viewer is provided with glasses having different colored filters in front of each eye. Each filter rejects the image that is not intended for that eye, and transmits the image which is intended to be seen by that eye. A red color filter will pass only the red image, while a blue/green color filter will pass only the blue/green image. If the left eye image is presented as a red image and the right as a blue/green image, and a blue/green filter is placed in front of the right eye and a red filter in front of the left eye, the proper images will be directed to the proper eye and a 3-D image will be perceived by the viewer.
The anaglyphic 3-D process is advantageously inexpensive to implement and can be used with any type of screen or display medium, as long as the colors can be effectively separated. Typically, two projectors are required, one for the red image, and another for the blue/green image. However, color filters which fully reject the undesired image are difficult to make, with the result that the 3-D effect is impaired. A significant disadvantage therefore remains in that the image is essentially interpreted in the brain as a black and white image or is only capable of producing drab colors at best, which is unappealing to the typical consumer. The images are generally of poor quality with perceptible shadowing, and may cause discomfort to the viewer, such as eye fatigue and/or nausea.
Another 3-D process used in motion pictures uses polarized light, in which the left and right eye images are separated by the use of polarizing light filters or other polarizing elements known in the art. The left eye image is projected onto the screen through a polarizing filter rotated by, for example, 45° to the left of vertical, while the right eye image is projected onto the screen through a polarizing filter rotated 45° to the right of vertical. In this way the polarization of the two images are at right angles, and similarly polarized filters placed in front of each of the viewer's eyes will cause the proper image to be transmitted to each eye. This method produces high-quality images, but disadvantageously also requires two projectors, goggles with high-quality polarizing filters for viewing, and a special polarization-maintaining projection screen. Moreover, the 3-D image will wash out if the viewer tilts his/her head too much or moves around too far.
Another technique which has been used to produce 3-D images of motion pictures involves the sequential presentation of left and right eye images to the viewer, wherein the alternate left and right eye images are projected so that the polarization of the two images is at right angles, at described above. To be perceived by the viewer as a continuous motion, each of the left and right eye images would need to be projected at twice the conventional frame rate of 24 frames/second. A single projector, for example, a digital light processing system (DLP) from Texas Instruments, capable of projecting 48 frames/second could be used to project the image with alternating polarization.
Another approach uses a field sequential technique. This is accomplished by means of sequentially recording the left and the right scenes (fields) and then sequentially displaying them in the same order with proper synchronization. Each viewer would be provided with synchronized electro-optical glasses to switch on the filter in front of each eye when its image is being presented. This process is complicated and expensive, and requires special equipment for broadcasting the trigger signals to the electro-optical glasses worn by each user.
It therefore becomes evident, that a full color 3-D television and/or multimedia display that can be viewed with relatively inexpensive glasses/goggles has mostly included generation of polarized images intended for the left and right eye by a projection method. Conventional methods to date have required a polarization-maintaining projection screen. However, the conventional methods cannot be used with, for example, rear-projection television (RPTV) sets, because the polarization becomes completely random when the image passes through the screen of the RPTV and as a result, the 3-D effect gets lost.
Accordingly, a new approach is required for displaying 3-D color television images with RPTV sets that do not rely on polarization effects to separate the images for the left and right eye.